Evaluation of Hitachi CAD to CD-SEM Metrology Package for OPC Model Tuning and Product Devices OPC Verification

摘要

Optical proximity corrections are widely used in semiconductor industry to compensate non-linear effects occurringrnwhen printing features smaller than exposure wavelength. Most advanced OPC software packages simulate opticalrnbehavior starting from a physical description of illumination and projection optics, while the characterization of resistrndevelopment and etch loading effects is still performed empirically, with different approaches that, generally, requirernthe collection of a huge amount of experimental data. Due to the wide variety of target patterns, which makesrnconventional CD-SEM recipe creation impossible, critical dimension (CD) measurements are usually performedrnmanually, requiring long time and, despite the attention paid while measuring, with poor guarantee of repeatability. Thernintroduction of 193nm resists, much more sensitive to SEM e-beam exposure if compared to 248nm materials, requiredrnincreased attention to be paid on both focusing and measuring phases in order to obtain reliable results. As well as OPCrnmodel tuning, the verification of correction effectiveness on product devices is performed almost in the same wayrnleading to the same kind of issues.rnIn order to overcome most of these problems ST is evaluating a new CD metrology package from HitachirnHigh-Technologies; this tool allows fully automatic CD measurements starting from GDS II coordinate input. Thernexact recognition of measurement locations is obtained through an algorithm, based on the superposition of the drawnrnGDS II layout to the SEM wafer images, which allows achieving high positioning accuracy.rnThe introduction of the tool significantly reduces measuring time down to the range of normal automated CDrnmeasurement times, while guarantying improved repeatability and optimized conditions even with 193nm resists due tornthe possibility of defining different structures for addressing and focusing before the measurement. This new systemrnopens new perspectives in OPC modeling giving the opportunity of a more accurate model tuning, required by 65 nmrntechnology node, and enables an extensive product devices OPC verification presently impossible due to time andrnprocedure issues.